The present invention provides a method of decorating a ceramic article. More particularly, the present invention provides a method of decorating a ceramic article using a heated ink composition comprising a metallic soap.
de Saint Romain, U.S. Pat. No. 5,273,575, Withington et al., U.S. Pat. No. 5,714,236, and pending U.S. application Ser. No. 09/479,350, now U.S. Pat. No. 6,402,823 each discloses ink compositions that generally consist of solutions of soluble metallic salts dissolved in one or more solvents. These ink compositions are intended to be applied to ceramic articles using ink jet printing techniques. Once applied in this manner, these soluble metallic salts in solution ink compositions are permitted to dry and then are fired to allow the metallic salts to decompose and form colored oxides or colored combinations with the material of the ceramic article upon which they are deposited. While these known ink compositions do make it possible to decorate ceramic articles using ink jet printing techniques, they also present some problems.
Many metallic salts, especially metallic carboxylate soaps, are viscous oils or waxy solids at room temperature (xcx9c25xc2x0 C.). In order to obtain an ink composition having the appropriate physical properties, such as viscosity, to allow for ink jet application, it has been the conventional practice to dissolve and dilute the soluble metallic salts in relatively large quantities of one or more solvents. The dissolution and dilution of these metallic salts with solvent reduce the concentration of the metal in the ink composition per unit of volume, thereby lowering the intensity of the decoration that can be obtained once the ceramic article has been fired.
In addition to problems relating to the intensity of decorations formed with such ink compositions, it will be appreciated that the use of relatively large quantities of solvents in prior art ink compositions presents other disadvantages. For example, it is difficult to disperse finely divided insoluble solid additives, especially inorganic mixed metal oxide pigments, in such prior art ink compositions because the solids tend to agglomerate and form sediments upon storage. Furthermore, the use of certain solvents can raise handling and environmental concerns. A method of decorating ceramic articles is needed that can overcome the disadvantages and limitations of the prior art.
The present invention provides a method of decorating a ceramic article using a heated ink composition comprising a metallic soap. The method according to the invention comprises: providing an ink composition comprising a metallic soap, said ink composition being a viscous oil or waxy solid at about 25xc2x0 C.; heating said ink composition to reduce its viscosity to less than about 40 centipoise; depositing micro-droplets of said heated ink composition upon said ceramic article; and firing said ceramic article in an oxidizing atmosphere to decompose the ink composition and form a coloring oxide.
The method of the present invention overcomes the limitations and disadvantages presented by prior art methods. For example, because the ink compositions used in the method according to the present invention contain relatively little, if any, solvents, the concentration of the metal applied to the ceramic article can be maintained very high, being limited only by the choice of ligand. Thus, it is possible to obtain decorations on ceramic articles that exhibit much greater intensity than was obtainable using prior art methods. Moreover, the ink compositions used in the method allow for the use of dispersed insoluble solid particles and other insoluble additives, which do not agglomerate or form sediments upon storage. Furthermore, since very little, if any, solvents are used, the method of the present invention presents far fewer handling and environmental concerns.
The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.